1. Field of the Invention
The present invention relates to a vehicle head lamp having a discharge bulb and more particularly to a head lamp for forming a sub-lamp luminous intensity distribution pattern.
2. Background
Since discharge bulbs are capable of high luminance irradiation, they have increasingly been adopted as light sources for vehicle head lamps in recent years.
In a head lamp equipped with such a discharge bulb, a sub-lamp luminous intensity distribution pattern, which is excellent in remote visual recognizability and has a wide is angle of irradiation, is obtainable when the sub-lamp luminous intensity distribution pattern has an oblique and a horizontal cut line.
There has been proposed a head lamp which is constructed so that a reflector having a reflective surface constituting of a plurality of reflective surface elements is used for forming such a sub-lamp luminous intensity distribution pattern, and the light reflected from the discharge bulb is controlled by each of the reflective surface elements.
FIG. 6(c) is a horizontal sectional view of three reflective surface elements 22As1', 22As2', 22As3' out of a plurality of reflective surface elements constituting a horizontal cut-line forming area 22A on the reflective surface of a reflector 16 having the aforementioned luminous intensity distribution control function; and FIG. 6(a) is a diagram illustrating a screen luminous intensity distribution patterns PA1', PA2', PA3' formed by the respective reflective surface elements 22As1', 22As2', 22As3'.
As shown in FIG. 6(b), the luminous intensity distribution patterns PA1', PA2', PA3' are those formed along a horizontal cut line CL2 and the left-hand end portions of the patterns are formed so as to extend up to the lower position of an oblique cut line CL1, whereby part of the hot zone (what is irradiated the brightest) HZ of the sub-lamp luminous intensity distribution pattern P for leftward luminous intensity distribution is formed.
The problems associated with this arrangement are as follows. As shown in FIG. 6(c), each of the reflective surface elements 22As1', 22As2', 22As3', . . . constituting the horizontal cut-line forming area 22A has a convex horizontal sectional shape. This is because the luminous intensity distribution design becomes relatively easy to make and the convex reflective surface is slightly more attractive than a concave reflective surface when the reflective surface is formed into the convex shape as the light reflected from each of the convex reflective surface elements is irradiated from the left-hand end portion to the left and also irradiated from the right-hand end portion to the right.
However, the following problems are posed when horizontal sectional shapes of the reflective surface elements 22As1', 22As2', 22As3', . . . are evenly made convex.
In a case where an extension 28 and the like are provided along the outer peripheral edge of the reflector 16 in front of the reflector 16 as shown in FIG. 6(c), for example, the light reflected from the left-hand end portion of the reflective surface element 22As1' positioned in the outermost side portion of the horizontal cut-line forming area 22A is shaded by the extension 28 and the like and is, therefore, not irradiated in the forward direction of the light fixture. Consequently, the luminous intensity distribution pattern PA1' formed-by the light reflected from the reflective surface element 22As1' becomes the pattern shown by the solid line with the slight wane of its left-hand end portion.
When the reflector 16 is aimed to the left, moreover, the light reflected from the left-hand end portion of the reflective surface element 22As1' is more shaded by the extension 28 and the like as shown in FIG. 6(c) and the luminous intensity distribution pattern PA1' formed by the light reflected from the reflective surface element 22As1' becomes a luminous intensity distribution pattern with the absence of the left half portion, as shown in FIG. 6(b). Thus, this luminous intensity distribution pattern PA1' contributes nothing to the formation of the hot zone HZ of the sub-lamp luminous intensity distribution pattern P. Further, the pattern PA1' results in the formation of a relative dark portion between the luminous intensity distribution pattern PA1' and the hot zone. Therefore, there arises a problem in that the sub-lamp luminous intensity distribution pattern P becomes a luminous intensity distribution pattern which makes it hard to visually recognize the remote forward field of the vehicle.
There have existed the foregoing problems in conventional head lamps using a halogen bulb, for example, as a light source but they still remain relatively minor. However, when a discharge bulb is employed as a light source, the aforementioned problems tend to become conspicuous because the discharge bulb forms an image entirely different in luminous intensity distribution characteristics from the halogen bulb.
More specifically, FIGS. 7(a) and (b) are diagrams illustrating luminous intensity distribution in the longitudinal direction of an image at a light source when light from the light source is reflected from one point of a reflector reflective surface 22 and emitted onto a front screen. As shown in FIG. 7(a), the luminous intensity distribution in the longitudinal direction of an image I' at the light source exhibits such characteristics that the luminous intensity gradually lowers in both its side portions when the light source is (the filament 18a' of) a halogen bulb. On the other hand, when the light source is (the light emitting portion (arc) 18a of) a discharge bulb, the luminous intensity distribution in the longitudinal direction of an image I at the light source exhibits such characteristics that the luminous intensity sharply drops at both its side portions as shown in FIG. 7(b).
When the image I having the luminous intensity distribution characteristics causing the luminous intensity in both end portions in the longitudinal direction to sharply drop is deflected or diffused along the horizontal cut line CL2 shown in FIG. 6(a), each of the luminous intensity distribution patterns PA1', PA2', . . . thus formed becomes a luminous intensity distribution pattern of high luminous intensity up to both end portions. In cooperation with extremely high power of the discharge bulb itself, both horizontal end portions of each of the luminous intensity distribution patterns PA1', PA2', . . . becomes very bright.
For the reason above, the dark portion formed between the luminous intensity distribution pattern PA1' and the hot zone HZ in FIG. 6(b) noticeably appears in comparison with the prior art head lamp using a halogen bulb or the like as a light source.
An object of the present invention made in view of the situation above is to provide a vehicle head lamp for forming a sub-lamp luminous intensity distribution pattern which is arranged so as to control light from a discharge bulb by a plurality of reflective surface elements constituting a reflector reflective surface, the head lamp making obtainable a desired sub-lamp luminous intensity distribution pattern while the reflector is being subjected to aiming adjustment.
In order to accomplish the above object of the present invention, a novel arrangement has been made for the arrangement of a reflective surface element which is positioned in the outermost side portion of a horizontal cut-line forming area.
According to the present invention, a vehicle head lamp comprising a discharge bulb and a reflector having a reflective surface constituting of a plurality of reflective surface elements for reflecting light from the discharge bulb forward so as to form a sub-lamp luminous intensity distribution pattern having an oblique and a horizontal cut line by controlling the light reflected from each of the reflective surface elements, is characterized in that (1) the reflective surface element positioned in the outermost side portion out of the plurality of reflective surface elements constituting a horizontal cut-line forming area on the reflective surface has a concave horizontal sectional shape and that (2) the reflective surface element adjacent to the inside of the reflective surface element in the outermost side portion has a convex horizontal sectional shape.
On condition that the reflective surface element "adjacent to the inside of the reflective surface element" in the outermost side portion has a convex horizontal sectional shape, it is not always necessary for (another or a plurality of other) reflective surface elements, which are positioned further inward and constitute the horizontal cut-line forming area, to have the convex horizontal sectional shape.
Since the reflective surface element positioned in the outermost side portion out of the plurality of reflective surface elements constituting the horizontal cut-line forming area of the reflector reflective surface has the concave horizontal sectional shape according to the present invention, rays of light incident on the reflective surface element from the discharge bulb are reflected forward in such a way as to cross each other.
Consequently, even though the light reflected from the outer end portion of the reflective surface element positioned in the outermost side portion is shaded by the extension and the like when the reflector is aimed outward, the luminous intensity distribution pattern formed by the reflected light emitted from the other portion of the reflective surface element in the forward direction of the lighting fixture without being shaded by the extension and the like becomes a luminous intensity distribution pattern with the leftover portion on the oblique cut-line side with respect to the original luminous intensity distribution pattern, so that this luminous intensity distribution pattern forms part of the hot zone of the sub-lamp luminous intensity distribution pattern and prevents a dark portion from being formed between the luminous intensity distribution pattern and the hot zone. Therefore, there is no possibility of allowing the formation of the sub-lamp luminous intensity distribution pattern which makes it hard to visually recognize the remote forward field of the vehicle even at the time of aiming.
Thus, in the head lamp for forming the sub-lamp luminous intensity distribution pattern so arranged as to control light from the discharge bulb by the plurality of reflective surface elements constituting the reflector reflective surface according to the present invention applied for patent, a desired sub-lamp luminous intensity distribution pattern is obtainable even in such a state that the reflector has been subjected to aiming adjustment.
With the arrangement above, the reflective surface element positioned in the outermost side portion and the reflective surface element (the second reflective surface element) adjacent to the inside of the reflective surface element in the outermost side portion are set to have substantially the same horizontal diffusion angle of reflection, whereby luminous intensity distribution control is made possible in that the second reflective surface element is used to form a luminous intensity distribution pattern to be formed originally by the reflective surface element positioned in the outermost side portion and with respect to the luminous intensity distribution pattern formed by the reflective surface element in the outermost side portion, it is utilized additionally for the hot-zone reinforcing purpose. Thus, a stable sub-lamp luminous intensity distribution pattern is formable, irrespective of the aiming position.
Incidentally, with respect to the reflective surface element positioned in the outermost side portion out of the plurality of reflective surface elements constituting the oblique cut-line forming area on the reflective surface, the luminous intensity distribution pattern formed by the light reflected from the reflective surface element generally forms part of the hot zone of the sub-lamp luminous intensity distribution pattern. Even though the light reflected from the outer end portion is shaded by the extension and the like at the time of outward aiming of the reflector because the reflective surface element is allowed to have the convex horizontal sectional shape, no dark portion may be formed between the hot zone and the luminous intensity distribution pattern formed by the reflected light emitted from the other portion of the reflective surface element in the forward direction of the lighting fixture without being shaded by the extension and the like. However, according to the present invention, the concave horizontal sectional shape of the reflective surface element causes the portion on the horizontal cut line side to be left as a luminous intensity distribution pattern with respect to the original luminous intensity distribution pattern at the time of outward aiming of the reflector to ensure that a sub-lamp luminous intensity distribution pattern for making it easy to visually recognize the remote forward field of the vehicle is secured even at the time of aiming.
When the reflector is aimed outward, a body side wall portion, a rim and any other members other than the extension may be considered as an object which shades the light reflected from the outer end portion of the reflective surface element positioned in the outermost side portion of the horizontal or oblique cut-line forming area. However, the extension is often provided along the outer peripheral edge of the reflector and even in this case, the reflected light tends to be shaded at the time of outward aiming. Therefore, according to the present invention, the constitution of the present invention is particularly effective when such an extension is provided in front of and along the outer peripheral edge of the reflector.